The present invention relates to a method for building up a moisture barrier in a soil so as to improve the nature of the soil by preventing the groundwater containing soluble salts from transudation toward the surface layer.
It is not rare that the soils of deserts or filled-in lands in a seacoast district contain a considerably large amount of salts such as sodium chloride detrimental to the growth of plants prohibiting the use of the land for agriculture. These salts are mobile in the soil and, even when the salt content in the portion of the soil at or near the land surface has been completely removed by one or other measures, evaporation of the water from the surface of the land in the daytime causes capillary action of the water in the depth of soil to ascend toward the surface layer bringing the salt as dissolved therein which again descends to the depth of the soil in the night or in a rainy weather to regain the original salty condition of the soil in the surface layer after repetition of the ascending and descending movements of the salt. Therefore, nature of a soil can be permanently improved only by taking a measure to prevent transudation of the salts in the depth of the soil toward the surface layer.
The conventional methods for the prevention of transudation of salts in soil include a method of spreading a plastic sheet in the soil underground, a method of forming a moisture barrier of asphalt underground and a method in which certain soil-solidifying agents, such as a cement milk, water glass, urethane, acrylamide, salts of acrylic acid and the like in the form of an aqueous solution or dispersion, are injected into the soil under pressurization through an injection nozzle inserted into the soil so that the soil is solidified by the interaction with such a soil-solidifying agent to form a water-impermeable layer underground.
These prior art methods are, however, not quite satisfactory from the standpoint of practicability. For example, the methods of spreading a plastic sheet and forming a moisture barrier of underground are time and labor-consuming because a large volume of the soil in the upper layer of the land must be grubbed up followed by returning the grubbed-up soil to the same area of the land so that these methods are practically applicable only to a very limited area of the land. The method of the injection of a soil-solidifying agent such as a cement milk is, on the other hand, also not free from disadvantages and practically not satisfactory because the process of the method is complicated involving the troublesome preparation of the solidifying agent and control of the conditions of injection and, in addition, it is important in this method in order to obtain satisfactory results that the injection must be performed at as many spots as possible all over the area of the land under treatment.